I recently purchased a 1987 560sl. I removed the parking brakes to make sure they would work when needed rotors and calipers were fine. When I went to reinstall the rear rotors the parking E-brake rotor wouldn't go back on. I readjusted the brake to the min. the rotor went on but required gentle persuasion when it did go on the rotor went backward but locked up going forward. Can someone help?